CCC 2070 The Ten Commandments belong to God’s revelation. At the same time they teach us the true humanity of man. They bring to light the essential duties, and therefore, indirectly, the fundamental rights inherent in the nature of the human person. The Decalogue contains a privileged expression of the natural law:
From the beginning, God had implanted in the heart of man the precepts of the natural law. Then he was content to remind him of them. This was the Decalogue.1

1 St. Irenaeus, Adv. haeres. 4, 15, 1: PG 7/l, 1012.